At least once a year, executives from Ciena Corp. spend a day at Johns Hopkins Hospital getting poked and prodded as they undergo tests for a barrage of potential ailments, from anemia to prostate cancer. They aren't necessarily feeling ill or showing any symptoms. In fact, the executives of Linthicum, MD-based Ciena are often healthy --- and their company wants to keep it that way. The $2,000-per-person prices for these full-body examinations are considered an essential corporate expense. Ciena and other companies with "executive health" perks say it's in their best interest to keep the top ranks well.